Recent studies show that many American adolescents, especially high school students, maintain schedules during the academic year that result in insufficient and ill-timed sleep. Behavioral factors contributing to the pattern are compounded by biological propensities. Students who obtain insufficient sleep, who are asked to perform when severely sleepy, and who have erratic sleep patterns may be at-risk for poor outcomes in a variety of domains. This project includes a comprehensive examination of adolescent sleep patterns in the context of measures that assess a variety of domains likely to be affected by poorly timed or inadequate sleep. Hence, this project will use a variety of measures and probes in cross-sectional and longitudinal paradigms to examine the types of vulnerabilities that may be specifically affected by sleep patterns. For the cross-sectional portion of the project in Study 1-Phase 1, the investigator plans to evaluate a representative sample of teenagers selected at random from the population to obtain a one-week snapshot portrait of sleep patterns using wrist actigraphy. Phase 1 of Study 1 provides data that determine more comprehensively the scope of problem sleep patterns and correlate sleep patterns with other measures obtained from self-report, school records, and parents. Study 2 involves a collaboration with the Center for Applied Research and Educational Improvement in the College of Education and Human Development at the University of Minnesota for a larger-scale assessment. This project will provide a Midwestern sample of adolescents that will allow the investigator to examine whether sleep patterns demonstrate regional similarities. This collaboration offers the potential to examine the impact of a schedule change on sleep patterns and other outcome measures. Many vulnerabilities that may associate with inadequate sleep and excessive sleepiness are low incidence events and therefore more amenable to longer term surveillance than acute cross-sectional assessment. Thus, in Study 1-Phase 2, students at high- and low-risk (based upon sleep patterns) are selected and followed across 16 weeks with daily field sleep assessments, weekly interviews, and probes for circadian phase and laboratory outcome measures at two time points. The studies outlined in this research plan for the first time will provide definitive data regarding the consequences of poor sleep patterns in adolescents, the relationship of sleep practices to the circadian timing system, and initial data concerning the impact of insufficient sleep upon emotion expression and regulation.